It is known that a metal titanate typified by calcium titanate or strontium titanate is added to a developer for electrophotography (Patent Documents 1 and 2). The reason for adding a metal titanate is that the metal titanate not only contributes to the prevention of occurrence of filming on the surface of a photosensitive member during image formation and the improvement in a cleaning property but also contributes to the improvement in electrostatic property because of its high-dielectricity.
However, a sufficient effect of improving the electrostatic property is not achieved even though metal titanate is added. For example, since metal titanate has relatively high resistance, the property of build up of electrification is low in an environment of low temperature and low humidity, even though metal titanate is added to the developer for electrophotography, and since metal titanate has high saturation charge amount, a toner having a high charge amount which has been adequately mixed and stirred and a toner having a low charge amount which has been rapidly supplied tend to be present together to broaden distribution of the charge amount in the case where images having a high coverage rate are printed after print images having a low coverage rate have been printed continuously, resulting in fogging or toner flying occurred or image density of a solid image was reduced. On the other hand, if the developer contains particles having low resistance for the purpose of improving problems in an environment of low temperature and low humidity, it was impossible to maintain good electrostatic property in an environment of high temperature and high humidity, and fogging occurred or the transfer property was deteriorated to reduce image density of a solid image when, for example, the developer was left standing for a long term.